1. Field of the Invention
The present invention relates to an ink supply mechanism that supplies ink from an ink container to an ink jet recording head. The invention also relates to an ink jet cartridge and an ink jet recording apparatus, which are provided with the ink supply mechanism.
2. Related Background Art
The recording apparatus, which is used as a recording apparatus for a printer, a copying machine, or a facsimile equipment, or which is used as an output device for a complex apparatus that includes a computer, a word processor, or for a work station, among some others. The recording apparatus is then structured to record images (including characters, symbols, or the like) on a recording material (a recording medium) such as a recording sheet or a thin plastic sheet (an OHP or the like).
The recording apparatuses thus structured are classified into various types, such as a ink jet type, a wire-dot type, a thermosensitive type, or a thermal transfer type, by a recording method of recording means adopted by each of them. Of those mentioned here, the recording apparatus of ink jet type (ink jet recording apparatus) is the one that records by discharging ink to a recording material from the recording head serving as recording means. This recording means is easily made compact, and also, with such compact head, highly precise images are made recordable at higher speeds. Here, among many other advantages, there is the one that recording is possible at a lower running cost on an ordinary recording sheet without any particular treatment given to it. Also, this apparatus is of non-impact type, making a lesser amount of noises, while producing color images with ease using multiple colors.
Here, in particular, the ink jet type recording means that discharges ink by the utilization of thermal energy makes it easier to manufacture the one having a highly precise arrangement of liquid paths (discharge ports) with the formation of the electrothermal transducing elements, electrodes, liquid path walls, ceiling plate, and others, which are provided on a substrate produced by means of film formation through etching, vapor deposition, sputtering, and other semiconductor manufacturing processes. Thus, the recording means is made compact still more in this manner. Also, utilizing the advantages of the IC technologies and the micromachining techniques the recording means can be elongated easily or its surfacing (two-dimensional arrangement) can be effectuated easily to make the recording means available in full multiple condition or to assemble it in a higher concentration.
The recording means of an ink jet recording apparatus described above is generally provided with an ink discharge unit that creates fine ink droplets; an ink supply unit that leads ink to the ink discharge unit; and an ink tank unit that stores ink in it. The ink tank unit is provided with a porous absorbent formed by urethane form or the like. Ink is absorbed and retained in such absorbent. Ink thus absorbed in the absorbent is not allowed to leak by means of the capillary force generated by the fine holes of the absorbent irrespective of the posture in which the ink jet recording head is placed. The ink tank is usable without staining the interior of the recording apparatus, the desk, the hands, or the like. Ink stored in an ink container of the kind is supplied to the recording head from the ink supply port provided for the ink container.
Nevertheless, with the ink tank thus structured, pigments are sedimented if the ink that uses pigments as colorants is stored in it for a long time, although there is no problem when the ink that uses dyestuffs as colorants is stored in it. Then, the uneven concentrations, that is, the concentrations that become different depending on locations, are caused to occur in the ink which is stored in the ink container.
Usually, the pigment ink is obtained by crashing finely the colorant which is insoluble to water after being mixed with copolymeric resin or the so-called interfacial active disperse agent, and then, diluted with water, oil, or some other solvent. The pigment particles themselves are not soluble to water. Therefore, when coated on a printed object, the pigment ink is superior to the dyestuff ink in terms of the water resistance. Further, the pigment particles withstand light well. As a result, the pigment ink is not discolored even if exposed to light for a long time. It demonstrates an excellent performance particularly with the printed object which should be shown on the wall or the like for a long time. This is because the pigment ink is widely used for general printed objects. However, although the fine solid particles, such as pigments, are allowed to float on liquid, its sedimentation should take place inevitably if the specific gravity thereof is greater than that of the solvent liquid (medium).
Here, the sediment speed of the particles can be expressed as follows:
u=2r2(xcfx812xe2x88x92xcfx811)g/9xcex7xe2x80x83xe2x80x83(1)
where r is the radius of the particle which is assumed to be spherical; xcfx811 and xcfx812 are the concentrations of the particle and medium, respectively; g is the gravitational acceleration; and xcex7 is the viscosity coefficient. The above expression (1) is called Stokes"" formula.
Also, besides receiving the sedimental action brought by the gravity, the particles are influenced by the thermal motion of the medium molecules, thus continuing the Brawnian motion without interruption. By the Brawnian motion, there occurs the diffusion which is the action opposite to the sedimental one. With this diffusion, it is intended to implement the distribution of the particles uniformly.
The perpendicularly concentrated distribution of the pigment ink contained in an ink container is determined by the aforesaid sedimental action and the diffusion brought by the Brawnian motion. Now, given the concentration of pigment ink on the bottom of an ink container as Co, the concentration C at a height h from the bottom can be expressed as follows:
ln (C/Co)=xe2x88x924xcfx80r3(xcfx812xe2x88x92xcfx811)gxc2x7h/3kTxe2x80x83xe2x80x83(2)
where r is the radius of the particle which is assumed to be spherical; xcfx811 and xcfx812 are the concentrations of the particle and medium, respectively; g is the gravitational acceleration; k is the Boltzman""s constant; and T is the temperature of the pigment ink designated by the absolute temperature.
Now, for example, if the radius r of the particle is 200 nm; the temperature of ink T is 27xc2x0 C.; the concentration of the particle xcfx811 is 1,400 kg/M3; and the concentration of the medium xcfx812 is 1,000 kg/M3, the ratio of concentration of 2% occurs per difference of 1 mm high. Also, if the viscosity of ink in this case is assumed to be 0.037 poise, it is calculated that the particle is sedimented to approximately 5 cm in two months, that is, the sedimental speed of the particle is worked out to be approximately 2.5 cm/month.
In practice, however, there is no appearance of such abrupt changes of concentration as indicated by the sedimental speed as described above. Conceivably, it is because of the constant convection current given to ink (liquid) stored in an ink container, which results in an even mixture eventually, and functions to prevent the occurrence of sediment of the particles.
In other words, the environment where an ink tank is kept is such as on a shelf in a room or in the interior of a printer located in a room. Therefore, an ink tank is always affected by the changes of the environmental temperature. The changes of the room temperature following the turning on and off of the air conditioning, and further, the temperature changes in the interior of a printer following the turning on and off of the printer power source may easily bring about the temperature changes of 40xc2x0 C. to 50xc2x0 C. Then, when a printer is on standby or in operation, the heat generation from the interior of the printer changes constantly following the turning on and off of a motor to drive the head, to enable the carriage to travel, and to carry a recording sheet, among some other operations. Therefore, the inner temperature is caused to change without interruption, which results in the repeated occurrence of the convection current in liquid stored in the ink tank placed under such environment. This has been reported in the publication xe2x80x9cThe fundamentals of the Colloid Chemistry p.35 and onxe2x80x9d by Masayuki Nakagaki and Kiyonari Fukuda (New fundamental chemistry series (5) edited by Nippon Chemistry Institute, and published by Dai Nippon Publications).
However, the convection current is considerably impeded by the ink which is absorbed into the absorbent of the ink container. Thus, the resultant mixture that follows the constant convection current is made impossible so that the sediment is allowed to occur eventually. Consequently, the uneven concentrations take place in ink in a stationary ink container. Here, for the ink supply port of an ink container, a cylindrical filter is provided in order to prevent dust particles from entering the nozzles of a recording head. Then, the diameter of the portion where the filter is in contact with an absorbent is made larger to a certain extent in order to reduce resistance to the ink flow. As a result, if the ink container is stationarily placed for a long time in a state where the diameter of the filter is directed perpendicularly, the ink the concentrations of which differ in the diameter direction of the filter is allowed to flow toward nozzles. If the concentration of ink is different at the ink supply port as in this case, the resultant densities of ink become different eventually when discharged from each of the nozzles on the nozzle array, thus allowing the uneven prints to appear on the portion requiring a higher printing duty. In other words, the difference in the ink concentration at the ink supply port and the density of ink discharged from each of the nozzles of the nozzle array of a recording head correspond to each other after all, although the degree of this correspondence becomes lower on the printed portion of a lower duty, which is not easily recognizable as the uneven pints.
The present invention is designed in consideration of the technical problems discussed above. It is an object of the invention to provide an ink supply mechanism which makes it possible to prevent the uneven concentration of ink contained in an ink container left intact for a long time, thus preventing the unevenness of the recorded images. It is also the object of the invention to provide an ink jet cartridge and an ink jet recording apparatus, which use such ink supply mechanism.
In order to achieve the objects described above, the ink supply mechanism of the present invention, which is provided with an ink supply path to supply ink contained in an ink container to an ink jet recording head for recording images on a recording medium by discharging ink from discharge ports, comprises agitating means provided for the ink supply path for agitating ink flowing in the ink supply path.
With the structure thus arranged, ink is supplied to the ink jet recording head in a state of being agitated by agitating means arranged in the ink supply path even when uneven concentrations occur in ink stored in the interior of the ink container which is left in tact for a long time, thus making it possible to uniformalize the concentrations of ink discharged from each of the discharge ports of the discharge port array of the recording head, and to record good images on a recording medium without unevenness of densities thereof.
Also, it may be possible to arrange the structure so that a plurality of extrusion groups formed by plural extrusions arranged in the circumferential direction in the ink supply path are arranged for the aforesaid agitating means in the direction of the ink flow, and that each of the extrusions of the adjacent extrusion groups is arranged in a position deviated from each other in the direction of the ink flow.
Further it is preferable to structure the aforesaid extrusions sa as to create ink flow in the circumferential direction of the ink supply path.
Furthermore, it may be possible arrange the structure so that the aforesaid ink supply path is provided with a tapered ink inlet port on the end portion on the ink flow-in side, and each of the extrusions is arranged on the inner face of the ink inlet port.
Also, the structure may be arranged so that a plurality of agitation members, which are provided with flow paths partitioned in the form of latticework, are arranged for the aforesaid agitating means in the direction of ink flow in the ink supply path, and the agitation members adjacent to each other are arranged to enable the direction of each latticework thereof to be deviated from each other with respect to the circumferential direction of the ink supply path. The ink supply mechanism thus structured, the ink flow is divided by the latticework when ink passes a certain agitation member. Then, the ink flow thus divided is further divided when passing the next agitation member. Therefore, when ink passes the plural numbers of the agitation members, ink is agitated eventually.
Further, it is preferable to arrange the structure so that the deviated angle of each latticework of the agitation members adjacent to each other is form at an angle of approximately 45xc2x0 in the circumferential direction of the ink supply path.
In addition, the structure may be arranged to provide the aforesaid ink container with an ink absorbent for absorbing ink.
Also, the aforesaid ink jet recording head may be structured to be provided with an electrothermal transducing element for generating thermal energy to be utilized for discharging the ink. Further, the structure may be arranged so that ink is discharged by the utilization of film boiling created by the thermal energy applied by the electrothermal transducing element.
Also, the ink jet cartridge of the present invention comprises an ink supply mechanism of the present invention described above, and an ink container that retains ink to be supplied to the ink jet recording head of the ink supply mechanism.
Further, it may be possible to arrange the structure so that the aforesaid ink container is provided with an ink absorbent for absorbing ink.
The ink jet recording apparatus of the present invention comprises the ink supply mechanism of the present invention described above, and driving signal supply means for supplying driving signals to enable the ink jet recording head to discharge ink therefrom.
Also, the ink jet recording apparatus of the present invention comprises the ink supply mechanism of the present invention described above, and recording medium carrying means for carrying the recording medium that receives ink discharged from the ink jet recording head.
Further, it may be possible to arrange the structure so that the ink jet recording apparatus of the present invention discharges ink from the ink jet recording head of the aforesaid ink supply mechanism to record images on the recording medium by the adhesion of ink thereto.